Conventionally, the household dehumidifier uses a refrigerant compressor to condense the moisture in the air to achieve dehumidification. However, the use of refrigerant results in problems such as ozone layer depletion. Therefore, there is the need in developing a novel dehumidification technique without using refrigerant.
In rotary desiccant dehumidification, the refrigerant compressor is not required; instead, an absorbing material is used to absorb the moisture in the air and then electrical-thermal heater is used to heat up the gas flow through a regenerating area of the absorbing material to desorb the moisture. The high-temperature and high-moisture gas through the regenerating channels is introduced into a heat exchanger for condensation. The condensed moisture is then collected by a water collector to achieve household dehumidification. Since dehumidificaton achieved by the rotary dehumidifier using an absorbing material is temperature and humidity independent and refrigerant free, it is advantageous in low noise and low cost without using the compressor.
In the rotary desiccant dehumidifier 1, as shown in FIG. 1, a moist gas flow 90 flows through a heat exchanger 10 into an absorbing material 11 so that the absorbing material 11 is capable of absorbing the moisture in the gas flow 90. The dehumidified gas flow 92 is released by a dehumidifying blower 12 to achieve dehumidification. On the other hand, an electric heater 13 heats up the temperature of a circulating gas flow 91. The water molecules in the absorbing material 11 is vaporized and desorbed by the temperature difference between the high-temperature circulating gas flow 91 and the water molecules in the absorbing material 11. Then, the high-temperature high-moisture circulating gas flow 91 enters the heat exchanger 10 to perform heat transfer with the low-temperature moist gas flow 90 at the entrance of the dehumidifier 1. The high-temperature high-moisture gas in the heat exchanger 10 can be condensed into liquid-phase water 93, which is then collected and exhausted. The circulating gas flow 91 returns to the electric heater 13 to repeat the aforesaid processes to complete moisture desorption. The absorbing material 11, the electric heater 13 and the heat exchanger 10 are integrated to achieve the dehumidification as a dehumidifier 1.
The absorbing material in a rotary dehumidifier is mostly porous. For example, the porous structure can be honeycomb type or corrugate type. Dehumidification uses physical absorption to absorb water molecules in the air by micro pores of absorbent to produce dried air. The absorbing capability of the rotary dehumidifier depends on, for example, the type and the amount of the absorbent, the temperature and humidity of the incoming air, the thickness of the rotary dehumidifier, the surface area of the honeycomb, the speed of the gas flow through the rotary dehumidifier, and the rotational speed of the rotary dehumidifier. A regenerating circulating flow channel is required to desorb the absorbed moisture from the dehumidifier. Therefore, dehumidification-regeneration is achieved by continuous absorption and desorption. The referred regenerating flow channel starts from the interface between the electric heater 13 and the absorbing material 11 (rotary dehumidifier) through the heat exchanger 10 and ends at the inlet where the gas flow enters the electric heater 13. For the absorbing material 11 (rotary dehumidifier), the gas flow inlet is a regeneration area of the rotary dehumidifier and the gas flow outlet is on the regeneration area wheel before the high-temperature and high-humidity gas enters the heat exchanger. In a rotary dehumidifier system, after the high-temperature and high-humidity gas on the regeneration side enters the condenser, heat exchange takes place between the high-temperature and high-humidity gas and the low-temperature gas outside the pipeline. Therefore, the high-temperature high-moisture gas in the condenser can be condensed into liquid-phase water.
In conventional rotary desiccant dehumidification, an electric heater is used to heat up the gas flow on the regenerating area to increase the temperature of the regenerating air. The thermal desorption mechanism comprises two approaches. One is vaporization by heat exchange of the gas flow, wherein a temperature gradient occurs as the circulating gas flow is heated up and the moisture is vaporized and desorbed from the absorbing material by the energy generated during heat exchange. However, this approach costs high power consumption to achieve dehumidifying because it takes a long time for vaporization to generate high-temperature gas required during moisture desorption. The other approach is vaporization by thermal radiation, wherein high-temperature gas is obtained by conducting a current flowing through a heating wire in the heater. Thermal radiation enables the water molecules in the absorbing material to receive the heat to be vaporized to desorb from the absorbing material. Since the radiated heat is proportional to the surface temperature to the power of four and the surface temperature of the electric heater is higher than 400° C., the radiated heat is very high. Therefore, the moisture desorption effect is much more important than vaporization by heat exchange of the gas flow. Accordingly, in the aforesaid two approaches, conventional desorption approaches by heating up the circulating gas flow or thermally radiating the water molecules to achieve desorption inevitably lead to high power consumption since the radiated heat is mostly absorbed by the absorbing material. Moreover, the radiated heat increases the surface temperature of the absorbing material, which adversely affects the absorption of water molecules by the desiccative to reduce the dehumidifying performance. Therefore, in a rotary dehumidifier, the power consumption is high and dehumidification efficiency is reduced.